Wireless communication devices such as cell phones and personal digital assistants (PDAs) have become increasingly common in recent years. One of the numerous features that these devices often incorporate is location determination. As a result, a wireless communication device carried by a person may function as a means of locating the person.
In particular, when a user in a wireless communications network initiates a communication session, the nature of the communication may necessitate locating the user. Commonly, a user must be located when the user places a “9-1-1” emergency telephone call. Other scenarios exist as well. For example, a user may contact a service provider requesting directions to nearby restaurants or to a gas station. To provide accurate information, the service provider must be able to determine the user's location.
The advent of cellular telephones required new locating technology. Previously, 911 calls originated mainly from landline telephones. Therefore, the process of determining the location of a caller was usually a simple matter of looking up the street address of the calling telephone number. Unlike landline telephones that were fixedly associated with particular street addresses, cellular telephones could place calls from anywhere within a cellular coverage area. Thus, a more complex system of position determination was required in order to determine the location of a calling cellular telephone.
To facilitate 911 services for cellular telephone callers, the United States Federal Communication Commission (FCC) mandated the implementation of “Enhanced 911” (“E911”) services. The E911 mandate was divided into two phases. According to Phase 1, the location had to be identified with an accuracy of at least cell and sector. As this information is typically maintained by a cellular wireless carrier in a subscriber's home location register (“HLR”), Phase 1 presented little technical challenge. According to Phase 2, the location must be provided with far more granularity than the cell and sector information maintained in the HLR. In response, the Telecommunications Industry Association (TIA) has proposed a standard entitled “Enhanced Wireless 9-1-1 Phase 2” or “J-STD-036-A” (including a recent addendum, J-STD-036-A-2002), the entirety of which is hereby incorporated by reference.
Accordingly, wireless communication devices (WCDs) are typically configured for Global Positioning System (GPS) connectivity in order to facilitate location determination. Ideally, a GPS signal would always be available to a WCD. In practice, however, non-GPS zones, which are locations where a GPS signal is not available from a GPS satellite, often exist throughout the coverage area of a radio access network (RAN). Typically, non-GPS zones exist where there is no line-of-sight between the satellite and the WCD. Therefore, indoor locations, such as a subscriber's home or business, typically create non-GPS zones.
In practice, the topology of a given sector often includes both non-GPS zones and zones where GPS is available. Further, multiple non-GPS zones may exist within a given sector of a RAN. For example, in an urban area, a sector that spans a number of city blocks may include both outdoor areas where a GPS signal is available, such as parks, sidewalks, streets, parking lots, etc., as well as indoor or covered areas, such as office buildings and parking garages, which create non-GPS zones in the same sector.